1. Field of the Invention
The present invention generally relates to a liquid crystal display device, and more particularly to a thin film transistor substrate of the liquid crystal display having light-shield device to prevent light leakage.
2. Description of the Related Art
Due to the advance of electronic technology, especially for the popularity of portable electronic products, the requirements of light, compact and low-energy consuming display are gradually increasing. With the advantages of low-energy consuming, low-heat dissipation, light-weight and non-luminescence, liquid crystal displays (LCD) have been widely used in the electronic products and even have replaced the traditional CRT displays.
An LCD basically consists of polarizers, glass electrodes and liquid crystal materials. The polarizers are made by sandwiching the polarizer material between two transparent films. The glass electrodes are made of high quality flat glass which is plated with a layer of conductive film of metallic oxidation. When the liquid crystal molecules are applied with electric field, they are easily re-arranged into a different alignment state, thereby resulting in different transmittance according to the electric field applied and displaying image in the LCD. The manufacturing process of LCD substantially includes the steps of injecting the liquid crystal material into the space between the two flat glasses with glass electrodes thereon, and adhering polarizer films onto the outer surfaces of the flat glasses so as to form the LCD cell. Then the driving circuits, controlling circuit, and backlight components, etc., will be assembled to constitute an LCD module.
Further, for conventional manufacturing processes of a thin film transistor (TFT) substrate, a tri-layer process or a back channel etch (BCE) process is employed for facilitating the TFT matrix. Conventionally, six to nine masking steps are required for both the BCE process and the tri-layer process so as to form a layered TFT structure on a glass substrate. In this TFT structure, disposed on the glass substrate are a first conductive layer and a second conductive layer in turn, and an insulation layer is sandwiched therebetween. The first conductive layer is used to form scan lines and gate electrodes of a TFT unit, and is generally referred to as “metal one”. The second conductive layer is used to form data lines and source/drain electrodes of a TFT unit, and is generally referred to as “metal two”.
The first and second conductive layers which are opaque are typically made of metal, such as chrome and aluminum, and cooperate with an Indium-Tin-Oxide (ITO) electrode on the perimeter (the out lead bonding region) of the TFT substrate to form terminals or leads. The first and second conductive layers are formed as parallel lines on the displaying region of the TFT substrate and the lines are gathered to form a plurality of terminal groups on the out lead region. The terminal groups are corresponding to tape carrier packages for electrically connecting to the driving circuits and/or the controlling circuits.
As shown in FIG. 1, it depicts a typical LCD module 10 provided with a metal frame 12. The LCD module 10 substantially comprises an LCD panel 14 and a back light module 16. The LCD panel 14 includes a TFT substrate 18 and a color filter (CF) substrate 20. The back light module 16 comprises a light source (not shown), a light guiding plate 22, and a multi-layer prismatic plate 24.
As shown in the drawing, the TFT substrate 18 is illuminated with the back light module 16 and a differential distance Ws exists between the real width and the ideal width W of the black matrix layer of the CF substrate 20. Therefore, the light may leak (shown by the arrow in the drawing) from the region between the metal frame 12 and the CF substrate 20. When the LCD module 10 is observed with an angle larger than θ, the leaking light may cause visibly bright lines in the edge of the metal frame 12. Also, on an outlead bonding region of the LCD module 10, the metal terminals are opaque and are gathered to form a plurality of groups corresponding to the driving circuits and the controlling circuits, so the uneven luminance is formed on the perimeter (the outlead bonding region) of the LCD module 10. This uneven luminance is corresponding to the location of the terminal groups. Further, because of the design of lightening the module and increasing the opening of the metal frame and the visible area, the problem of the light leakage became more serious.
Thus, U.S. Pat. No. 5,850,275 entitled “Liquid Crystal Display” issued on Dec. 15, 1998 to Watanabe et al., incorporated herein by reference, discloses a liquid crystal display having a light shield material provided on regions adjacent to but not touching the terminal groups and the outgoing line groups to decrease this uneven luminance on the perimeter of the LCD. However, the light shield area is formed with the same materials as that of the terminals and the outgoing lines in the same process simultaneously, i.e. the light shield area, the terminals and the outgoing lines are constituted by the same metal layer. Therefore, the light shield area mentioned above cannot be formed between the lines, so the problem of the light leakage on the edge of the LCD module still has not been solved.
Accordingly, there exist needs for providing a suitable device for preventing the light from leaking through the out lead bonding region on a TFT substrate of an LCD, thereby providing the even luminance on the edge of the LCD.